JP2007-334898(A1) discloses a data delivery system including a reception section that receives, from a plurality of clients, request information having identification data of the clients in a predetermined period of time, a test section that identifies the plurality of clients based on the identification data, an alarm section that generate an alarm signal about the clients who are yet to transmit the request information in the predetermined period of time, a generation section that generates response data for an arbitrary one of the clients who is identified by the test section, and a transmission section that transmits the response data to the arbitrary client.